The low-mass diskless population of Corona Australis

¹ Laboratorio de Astrofísica Estelar y Exoplanetas, Dpto. Astrofísica, Centro de Astrobiología (LAEX-CAB), CSIC-INTA, ESAC Campus, PO Box 78, 28261 Villanueva de la Cañada, Madrid, Spain e-mail: belen@cab.inta-csic.es
² Research and Scientific Support Department, European Space Agency (ESTEC), PO Box 299, 2200 AG Noordwijk, The Netherlands
³ Herschel Science Centre, European Space Agency (ESAC), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁴ Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA
⁵ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany

Received: 23 November 2009
Accepted: 12 March 2010

Abstract

We combine published optical and near-infrared photometry to identify new low-mass candidate members in an area of about 0.64 deg² in Corona Australis with the S-parameter method. Five new candidate members of the region are selected. They have estimated ages between 3 and 15 Myr and masses between 0.05 and 0.15 . With Spitzer photometry we confirm that these objects are not surrounded by optically thick disks. However, one of them is found to display excess at 24 μm, thus suggesting it harbors a disk with an inner hole. With an estimated mass of 0.07  according to the SED fitting, this is one of the lowest-mass objects reported to possess a transitional disk. Including these new members, the fraction of disks is about 50% among the total Corona Australis population selected by the same criteria, lower than the 70% fraction reported earlier for this region. Even so, we find a ratio of transitional to primordial disks (45%) very similar to the value derived by previous authors. This ratio is higher than for solar-type stars (5–10%), suggesting that disk evolution is faster in the latter, and/or that the “transitional disk” stage is not such a short-lived step for very low-mass objects. However, this impression needs to be confirmed with better statistics.